Is an atonement or making up of prayers required of a mother if she rules that a group which insults the Companions and deifies other than Allah is not Muslim?

There is no sin upon your mother if she describes those who deify other than Allah the Almighty or insult the Companions as not being Muslims. For whoever insults the Companions is not among the Muslims in their character, as the Prophet, peace and blessings be upon him, said: "The believer is not a slanderer, nor a curser, nor an obscene speaker, nor an ill-mannered person," and "Insulting a Muslim is a transgression."